Hello all I'm wanting to start a new project but need a little help from someone more experienced in reading and creating schematics. This amp The Shell Manhasset or 2020P is one I own but it has some issues and I'd like to recreate a simpler version of it. What I want to do is remove some of the bells and whistles so to speak. If someone could look at the schematic and redraw it with only one input and remove the loudness, low pass filter, and all the selector knobs. As well as the electric eye circuit to make it a basic amp it would be greatly appreciated. I know it's asking a lot but I thought maybe someone would like a challenge. Oh and there is a mistake in the schematics which show 12ax7 12au7 12ax7 as the drivers but they must have made changes at some point because the amp actually has 12ax7 12au7 12au7 tubes in it as well as factory printing on the amp matching that. Not a big deal but thought I'd mention it.
So anyone up for the challenge ?
So anyone up for the challenge ?
Cut the caps C15, C28 off the "Low Filter" switch and those terminals become preamp out and amp in. Add two RCA connectors for amp in. Loudness switch can be left as-is or you can solder a jumper across the "off" terminals. You can unplug V2, V3, V10, but V1's heater is part of the cathode resistor for the output tubes.
No not phono. It will either be a tuner or a Wiim. Wiim is a networked player it allows you to access a bunch of online content as well as bluetooth connections.
Wait I do not want to change the amp I own it plays fine but has issues with some of the ancient potentiometers sounding scratchy when you turn them, deoxit helped but not completely. I want to build a totally separate amp but without some of the features in the schematics.
Strip it all down and rebuild your own way.
Or sell the piece and buy your own parts to replicate(clone) it.
I think a lot of people would like such a piece to restore and adore.
They would tell you to buy some transformers, an aluminum shell, a few chunks of wood or whatnot, some caps and resistors and roll your own.
I would side with them, I think.
I don't know if your unit is collectible but it is most likely worth more restored than torn up.
Or sell the piece and buy your own parts to replicate(clone) it.
I think a lot of people would like such a piece to restore and adore.
They would tell you to buy some transformers, an aluminum shell, a few chunks of wood or whatnot, some caps and resistors and roll your own.
I would side with them, I think.
I don't know if your unit is collectible but it is most likely worth more restored than torn up.
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Something like this should work for the preamp section, easy to build. One dual triode for stereo.
My suggestion was to try the amp alone with the minimum of changes, a few minutes work and it can easily be returned to its original state. If volume from the tuner is adequate, no preamp is needed (Wiim is likely higher). If you want to rebuild it on a new chassis, you can use the amp section from the schematic with new capacitors. The 12AX7 heater in the cathode circuit would be replaced with an 82 Ohm, 5W (or more) resistor.
You guys are awesome!! Thank you for helping out.
Just curious (i have never designed an amp)
Why remove the pre amp 12ax7 12au8 12au7? Is it not needed. Was it only used for phono in?
I will keep you all updated on the experiment as i have most of the parts for this, just have to order some output transformers. I dont think i have any suitable pp transformers in my junk box.
Just curious (i have never designed an amp)
Why remove the pre amp 12ax7 12au8 12au7? Is it not needed. Was it only used for phono in?
I will keep you all updated on the experiment as i have most of the parts for this, just have to order some output transformers. I dont think i have any suitable pp transformers in my junk box.
First two are the phono / tape head preamplifer - not used for line-level sources. Third stage makes up for the losses of the tone controls.
Yes, 82 in parallel with 200, or the equivalent 60 or 62 Ohms replacing both (though neither of those values will be easy to find).
My math says 42 ohm?
Approx 6.3 volts across pin 4 and 5 of the 12 volt heater would yield 0.15 amps = 42 ohm equivalent on a 12AX7 valve.
I could be wrong...
